Implantable electrical stimulation systems have proven therapeutic in a variety of diseases and disorders. For example, spinal cord stimulation systems have been used as a therapeutic modality for the treatment of chronic pain syndromes. Peripheral nerve stimulation has been used to treat incontinence, as well as a number of other applications under investigation. Functional electrical stimulation systems have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Stimulators have been developed to provide therapy for a variety of treatments. A stimulator can include a control module (with a pulse generator), one or more leads, and an array of stimulator electrodes on each lead. The stimulator electrodes are in contact with or near the nerves, muscles, or other tissue to be stimulated. The pulse generator in the control module generates electrical pulses that are delivered by the electrodes to body tissue.
Conventional implanted electrical stimulation systems (including, for example, implantable leads and implantable pulse generators) are often incompatible with magnetic resonance imaging (“MRI”) due to the large radio frequency (“RF”) pulses used during MRI. The RF pulses can generate transient signals in the conductors and electrodes of an implanted lead. The lead captures RF energy and transmits it to the two ends causing at least the following two effects (a) the RF heating at the lead electrode to patient interface (b) damage to the IPG electronics due to conducted RF. Several factors affect the amount of RF energy captured by the lead like incident field, lead design, lead construction, lead shape, lead trajectory, presence of other elements or materials in proximity, lead length, frequency of RF signal, loading at the un-insulated ends, and the like.